Molecular Imaging Insight - May 2008 - (Page 17) Read more on Siemens TrueD ADDITIONAL RESOURCES: The past decade, however, has delivered tremendous advances on both sides of the radiation therapy process. On the imaging side, sophisticated acquisition techniques more clearly delineate tumors and margins. Plus, advances in treatment such as intensity-modulated radiation therapy (IMRT) and respiratory gating translate into ultra-precise treatments, sparing normal tissue and more accurately bombarding malignancies. 2008 brings new advances to further fine-tune radiation therapy protocols. For example, sites around the world are turning to Siemens Medical Solutions molecular imaging suite as the cornerstone of next-generation radiation therapy. Enabling technologies include Siemens Biograph 16 and 64 PET•CT scanners and Siemens Multimodality workstation with syngo TrueD software. The forefront of clinical research The Department of Radiation Oncology at University of Maastricht (MAASTRO) in Maastricht, The Netherlands, stands at the forefront of clinical research detailing the advantages of PET/CT in radiation oncology. The clinic deployed Siemens Medical Solutions Biograph 16 PET•CT scanner in 2002, becoming the first global site to use a hybrid system for radiation therapy simulation. Since August 2007, the department has used Biograph 40 TruePoint PET•CT; the higher resolution system allows respiratory correlated PET/CT. It is also on the cutting edge of research in the use of syngo TrueD software to improve tumor delineation, which, in turn, allows physicians to more tightly refine treatment margins and radiation dose within the tumor. The clinic’s first research project was designed to answer a basic question in functional imaging, says Professor Philippe Lambin, MD, PhD. That is, does PET/CT provide better visualization of lung tumors than standard CT simulation? Researchers found that PET/CT did provide better visualization. “We found that tumor volume is generally smaller on PET/CT than on CT, and, in many cases, there are discrepancies between CT findings and PET/CT results. Either CT misses some areas that light up on the PET study, or PET/CT detects cancerous activity missed by the conventional CT scan,” explains Lambin. The findings enabled researchers to improve treatment for lung cancer patients by irradiating more accurately the macroscopic tumor and reducing the amount of normal tissue irradiated during the radiation therapy treatment course (de Ruysscher et al, 2005). The next study, a prospective trial, analyzed outcomes of patients with discrepancies between PET/CT and CT findings. It’s not uncommon for PET/CT results to contradict CT findings. For example, CT often indicates cancerous activity in a patient’s lymph nodes, but the nodes do not light up as cancerous on the PET/CT study. That’s because CT may detect inflammations or scar tissue, which are not uncommon in patients with compromised lungs. PET/CT, however, analyzes functional content of tissue to more accurately identify cancerous areas. Conventional protocols treat CT-positive lymph nodes with radiation. Maastro Clinic designed a multi-year trial to determine if MolecularImaging.net bypassing treatment of these nodes presented a risk of recurrence to patients and recently reported that it is safe to forego treatment on lymph nodes identified as positive on CT and negative on PET/CT. Another trial, recently completed, built on this finding and treated patients, not with a fi xed dose (“the same radiation dose for all the patients”), but at an isotoxic level (“the same risk of complications for all the patients, but a different tumor dose for each”). This approach allows physicians to take advantage of PET/CT to determine small treatment volumes and escalate the tumor dose, in some patients until 80 Gy without increasing the risk of complications. This trial using sequential chemo-radiotherapy shows promising results with survival at two years above 47 percent in nonsmall cell lung cancer stage III, a result that compares very favorably to results of randomized trials with concurrent chemo-radiotherapy. The enabling technologies for Maastro Clinic’s advances include Siemens’ hardware and software, says Lambin. Biograph 40 TruePoint PET•CT allows the clinic to provide respiratory gating as the standard of care for lung cancer patients. “Respiratory gating allows us to individualize, based on tumor movement, the safety margin around the tumor (Bosmans et al, 2006). Acquiring respiratory gated PET/CT images, then auto-contouring based on Standard Uptake Values (SUV) on the gated studies in syngo TrueD and sending structures to our planning system allows us to define more accurately the area to irradiate, decrease the volume of irradiated area and escalate the dose to improve outcome,” says Lambin. Siemens’ software overcomes another major challenge in radiation therapy workflow. Conventional programs are plagued by variability in tumor delineation among various physicians. That is, tumor delineation is a human process prone to human error. Maastro Clinic uses Siemens TrueD treatment planning software to automate measurements, minimizing temporal discrepancies and variability among physicians. “The gold standard— pathological findings—show that this software is doing very well, but next to that it also shows that consistency among physicians is much better with autodelineation software, such as TrueD [van Baardwijck et al, 2007]. It provides a more homogeneous delineation, which is useful in clinical practice and for clinical trials. We use autodelineation routinely for lung cancer and we are currently investigating its value for rectal, cervical, and head and neck cancer,” sums Lambin. Collaborative pioneers Copenhagen University Hospital in Denmark pioneered the use of PET for radiation therapy treatment planning in 2001. Geography facilitated the approach with a PET scanner located adjacent to the radiation oncology department. The program first focused on head and neck cancers and then began using the hybrid scanner for cervical cancers. “We decided to use whole-body PET/CT rather than abdominal PET scans and found that 30 percent of cervical cases had more cancer than we thought,” reports Anne Kill Berthelsen, MD, chief physician, May 2008 | Molecular Imaging Insight 1 http://www.medical.siemens.com/webapp/wcs/stores/servlet/ProductDisplay~q_catalogId~e_-11~a_catTree~e_100010,1007660,1004808,1004804,1005404~a_langId~e_-11~a_productId~e_145341~a_storeId~e_10001.htm http://MolecularImaging.net
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.